Iranian Princess Ashraf Pahlavi, the twin sister of the last shah of Iran, has died at the age of 96.

Her death was announced by Reza Pahlavi, a son of the shah, in a Facebook post late on January 7.

Robert F. Armao, an adviser to the princess, was quoted by The New York Times as saying the cause of the death was "old age."

The princess was known as a close ally of her brother, Shah Mohammad Reza Pahlavi, and has always defended his rule.

According to a long-classified CIA account first published in 2000, the princess played a crucial role in the British- and U.S.-inspired military coup that overthrew Prime Minister Mohammad Mossadegh in 1953 and restored her brother to the throne.

Princess Ashraf focused on women's rights during an appointment to the UN, even as Iran's secret police were accused of torturing political activists under her brother's rule.

She was criticized for alleged corruption during her brother's rule.

The princess and her sister, Shams, were among the first Iranian women to go in public with their hair uncovered, breaking traditional norms in the conservative society.

After her brother's overthrow in 1979, Princess Ashraf left Iran and lived between homes in Paris, New York, and Monte Carlo.

She published a memoir and remained outspoken immediately after leaving the country, but gradually faded from public view in later years.